Cast single crystal components may suffer from surface breaking secondary grains, or defects. These surface breaking secondary grains, or defects have a minimum size of the order of 0.008 inch diameter (0.20 mm). At present there is no known apparatus or method which is capable of rapidly detecting and characterising these surface breaking secondary grains, or defects, in cast single crystal components, so that it may be incorporated as a step in the manufacturing process for the production of cast single crystal components. Cast single crystal components may suffer from surface breaking secondary grains, or defects, such as secondary grain boundaries, slivers, equiaxed grains, freckles, recrystallised grains, secondary grains, zebra grains and striations, which all differ in surface dimensions and crystal orientation relative to the main single crystal.